无法使用WebConfigurationManager.AppSettings检索值

我在c#中使用。net和mvc3。我有一个网站。

我需要检索<add key="sitelocalization" value="en-GB" />的值。

使用下面的代码，我收到这个错误:

String reference not set to an instance of a String.
Parameter name: name
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 
Exception Details: System.ArgumentNullException: String reference not set to an instance of a String.
Parameter name: name

在这一行thread . currentthread . currentuicculture = new CultureInfo(localization);

---

<appSettings>
    <add key="webpages:Enabled" value="false" />
    <add key="sitelocalization" value="en-GB" />
</appSettings>

        string localization = WebConfigurationManager.AppSettings["sitelocalization"];
        Thread.CurrentThread.CurrentUICulture = new CultureInfo(localization);
        Thread.CurrentThread.CurrentCulture = new CultureInfo(localization);

System.Configuration.Configuration rootWebConfig1 =
                System.Web.Configuration.WebConfigurationManager.OpenWebConfiguration(null);
            if (rootWebConfig1.AppSettings.Settings.Count > 0)
            {
                System.Configuration.KeyValueConfigurationElement customSetting = 
                    rootWebConfig1.AppSettings.Settings["customsetting1"];
                if (customSetting != null)
                    Console.WriteLine("customsetting1 application string = '"{0}'"", 
                        customSetting.Value);
                else
                    Console.WriteLine("No customsetting1 application string");
            }


<appSettings>
  <add key="customsetting1" value="Some text here"/>
</appSettings>